(1) Field of the Invention
The present invention relates to a transport device configured to transport a printing medium such as web paper in a given direction for printing and an inkjet printing apparatus having the transport device.
(2) Description of the Related Art
Examples of such the apparatus of this type conventionally include a printing apparatus having a plurality of measuring sections, a plurality of transporting sections, and a controller. The printing apparatus performs printing while transporting strip web paper on a transportation path. See, for example, Japanese Patent No. 4722631A.
The plurality of measuring sections measures tension of the web paper at a plurality of portions on the transportation path. The plurality of transporting sections transports the web paper adjacent to each of the plurality of measuring sections. The controller controls each of transportation speeds of the plurality of transporting sections in accordance with measurement results from the plurality of measuring sections. Here, the controller controls a transportation speed of one of the plurality of transporting sections on the most upstream side of the transportation path such that a measurement result from the measuring section adjacent to the transporting section is made close to a given value. In addition, the controller controls transportation speeds of the others of the plurality of transporting sections such that measurement results from the measuring sections on upstream and downstream sides of the transporting sections other than the basic shaft transporting section are close to the measurement result from the measuring section on the upstream side. This allows application of constant tension to the web paper at a plurality of portions on the transportation path.
However, the example of the conventional apparatus with such a construction has the following problem.
Specifically, the conventional apparatus adopts the transporting section on the most upstream side of the transportation path as a basic shaft. The conventional apparatus controls the transportation speed of the transporting section on the upstream side such that each of the transporting sections has measurement result on tension with a desired value. This enables balance of the transportation speed on the transportation section in an accelerating interval and a constant interval. The transportation speed of the web paper increases in the accelerating interval, whereas the transportation speed of the web paper is constant in the constant interval. However, in a decelerating interval where the transportation speed of the web paper decreases, the transportation speed on the transportation section may be non-uniform occasionally. This causes such a possible problem that irregular slack or damages may occur in the web paper.